"Say out-loud the color of the word" is the typical instruction in the Stroop Task. The trick is that when when green is in green font, people have no problem with answering correctly under time pressure. However, when green is in red font, people stumble because we read faster than we think about the color. Illiterate people have no problem with correctly naming the color of the word, as they can't read.
The Stroop Task is used in psychology experimental studies and, in the huge majority of cases, is irrelevant in the real world.
However, I came across a case in which the Stroop effect influences real-life interactions of customers (passengers) with a service.